In the prior art several types of apparatuses are used for coating a surface of a substrate. When the substrate is coated in a roll-to-roll apparatus the substrate needs to be transferred along a transport path which comprises rollers or other types of guiding elements. The surface of the substrate on which the coating is applied may in some cases be so sensitive that transportation through the path may contaminate or otherwise harm the surface before the coating is applied or the coated surface may be destroyed by the guiding elements.
In the prior art several types of apparatuses, and nozzle heads are used for subjecting a surface of a substrate to successive surface reactions of at least a first precursor and a second precursor according to the principles of atomic layer deposition method (ALD). In ALD applications, typically two gaseous precursors are introduced into the ALD reactor in separate stages. The gaseous precursors effectively react with the substrate surface, resulting in deposition of a single atomic layer. The precursor stages are typically followed or separated by a purge stage that eliminates the excess precursor from the surface of the substrate prior to the separate introduction of the other precursor. Therefore an ALD process requires alternating in sequence the flux of precursors to the surface of the substrate. This repeated sequence of alternating surface reactions and purge stages between is a typical ALD deposition cycle.
When making sensitive coatings, for example high quality barrier films, it is very important not to touch the clean side of the substrate before coating is applied or the coated surface after the coating. In this application ALD-head is an example of a deposition head. Other possible deposition and surface modification methods and deposition heads comprise CVD-coatings and related heads, PVD-coating and related heads, sputtering coating and related heads, aerosol coatings and related heads, or coatings effectuated by high energy zone like flame or plasma, and related heads. This invention relates especially to a roll-to-roll application, in which the substrate to be coated is arranged in a first roll that is unwound and transferred through at least one coating unit in which the coating is applied to the surface of the substrate and finally the substrate web is rewound to a second roll. Making a transport path in a roll-to-roll apparatus where a substrate is transferred from the unwinder roll to the rewinder roll without the clean side of the substrate or the coated side of the substrate facing any support structures is basically impossible.